1. Field of the Invention
The present invention relates to fiber optic communications. More particularly, the present invention relates to an attenuator capable of attenuating a light intensity of a signal carried by a fiber optic cable.
2. Description of the Related Art
Attenuators for fiber optic signal communications are known in the background art. A typical attenuator, such as used with a physical contact (PC) type connector, is formed as a clear glass or plastic disc. Generally, a connector of the fiber optic cable has a ferrule and the light transmitting optic fiber passes through a center of the ferrule to a polished end. When the connector is attached to a piece of equipment the polished end of the ferrule, with the light carrying optic fiber end thereat, is placed adjacent to a receiving detector lens or matching ferrule of the equipment.
If the light intensity is too great and needs to be attenuated, a clear or coated glass disc or plastic disc is inserted between the polished end of the connector ferrule and the receiving ferrule of the equipment. Attenuation occurs because of the increased spacing between the polished end of the connector ferrule and the receiving ferrule of the equipment, or perhaps also because of an absorption of light by the disc.
U.S. Pat. No. 4,261,640, which is herein incorporated by reference, illustrates an embodiment of the prior art attenuator. As illustrated in FIGS. 1-3, the prior art attenuator includes a cylindrical light absorbing filter disc 10, coupled between a first optic fiber 12 and a second optic fiber 14. The coupling is done so that an end 16 of the first optic fiber 12 is adjacent to a first surface 18 of the filter disc 10, while an end 20 of the second optic fiber 14 is adjacent to a second surface 22 of the filter disc 10. The first and second surfaces 18 and 22 are parallel to one another so that the facing ends 16 and 20 of the optic fibers can be directly in line with one another to insure maximum light transfer between them.
The coupling is accomplished by means of layers of a matching gel 24 and 25 which are coated respectively on the first and second surfaces 18 and 22 of the filter disc 10. First and second ferrules 26 and 27 are provided around each of the optic fibers 12 and 14, respectively, for protective purposes. The first ferrule 26 might be incorporated into a connector at the end of a patch cord, whereas the second ferrule 27 might be incorporated into a jack on a piece of equipment. The filter disc 10 may be manufactured at a certain thickness and/or with a certain tinting so as to absorb a given amount of light to attenuate an optical signal by a prescribed dB level.
Referring now to FIG. 2, a close-up exploded view of the first and second ferrules 26 and 27 incorporated into a connector and a jack, respectively, is shown. A first fiber optic cable 44 has the first optic fiber 12 terminated to the first ferrule 26, which is housed within a connector housing 28. The second optic fiber 14 within the second ferrule 27 is held in a jack housing 30. The filter disc 10 is located in a depression 32 in an end surface 34 of the connector housing 28 so that the first surface 18 of the filter disc 10 rests on a recessed surface 36 formed by the depression 32. The second surface 22 of the filter disc 10 faces outward from the connector housing 28 toward the jack housing 30. To provide for secure holding, the shape of the depression 32 should conform to the shape of the filter disc 10.
As can be seen from FIG. 3, the depth of the depression 32 is also generally set to correspond to the thickness of the filter disc 10 so that the second surface 22 of the filter disc 10 will be even with the end surface 34 of the connector housing 28. The connector housing 28 is also provided with an opening 38 extending along the longitudinal axis of the connector housing 28 from the recessed surface 36 toward an opposite end surface 40 of the connector housing 28. This opening 38 serves to hold the first ferrule 26 with its end 16 abutted against the surface 18 of the filter disc 10. To provide for maximum contact alignment, the opening 38 should be perpendicular to the plane of the recessed surface 36. It should be noted that a portion 42 of the opening 38 is enlarged to accommodate a jacket of the first fiber optic cable 44.
The jack housing 30 is also provided with an opening 46 for holding the second ferrule 27. This opening 46 extends along the longitudinal axis of the jack housing 30 from a recessed end surface 48 of the jack housing 30 facing the end surface 34 of the connector housing 28 toward an opposite end surface 50 of the jack housing 30. And, as in the case of the opening 38, the opening 46 also includes an enlarged portion 52 for a jacket of a second fiber optic cable 53. The second ferrule 27 is held in the opening 46 so that its end 20 is even with the recessed end surface 48.
To hold both the first and second ferrules 26 and 27 securely in their respective openings 38 and 46, set screws 54a, 54b, 56a and 56b are provided to extend through the wall of the housings 28 and 30 to press against the jackets of the first and second fiber optic cables 44 and 53. These set screws 54a, 54b, 56a and 56b prevent both rotational and longitudinal movement of the optic fibers 12 and 14 relative to the housings 28 and 30.
Coupling the first and second housings 28 and 30 together can be conveniently accomplished by using external threading 58 on a cylindrical portion 60 of reduced diameter of the connector housing 28 and matching internal threading 62 along the cylindrical wall leading to the recessed end surface 48 of the jack housing 30.
The filter disc 10 can be readily interchanged simply by decoupling the first and second holders 28 and 30 from one another, removing the filter disc 10 and installing a new filter disc 10 having a different degree of attenuation, and recoupling the first and second housings 28 and 30.